Laura Jeanne Reese Witherspoon was and remains Southern gentry - she's unmistakably blonde, she's 5ft 2in, and she has learned across her 30 years to make fun of her southern accent but, never forget, she is Scarlett O'Hara material, and every bit as tough in a fight. One of her ancestors, John Witherspoon, has his signature on the Declaration of Independence, and she's the child of a military surgeon and a mother with a PhD in paediatric nursing. Born in New Orleans, she was raised in Nashville (which has a thick social crust), and sent to Harpeth Hall, a select all-girls private school. From there she went to Stanford and was on her way to a degree in English when she took a leave of absence.

She was a very pretty child and a knock-out teenager, and that had got her into modelling, and more. At 15, she delivered a brilliant performance in Robert Mulligan's film, The Man in the Moon. It's still as searching and tender as anything she's done. She did graduate high school, but she was working very hard: a teen adventure film set in Africa, A Far Off Place; Jack the Bear; SFW; and Fear, in which she falls for older guy, and psycho, Mark Wahlberg.

Fear was not exactly what Harpeth Hall was training nice Nashville girls for, but it was elementary next to Freeway, the first truly distinctive Witherspoon film. It's a modern version of Little Red Riding Hood, directed by Matthew Bright, in which the wolves of the world need armed protection against trashy teen Vanessa Lutz. Freeway is still not widely known, but it is a great modern comedy, a vicious spin on the folklore of the road, and a fair estimate of the cultural pulp in which our young generation has been able to grow up.

Fear and Freeway made Witherspoon hesitate at Stanford. Instead, in the next few years, she had a lovely spot in Twilight, made Pleasantville, Cruel Intentions (co-starring with husband-to-be Ryan Phillippe) and Tracy Flick in Election, one of the great monsters of American self-righteousness. Some of us long for the sequel where Tracy goes to Washington and takes over the country.

Which brings us to 1999. Witherspoon was married and in demand. But some voices seem to have asked out loud, "What's a pretty southern girl like Laura Jeanne doing playing all these hard-ass girls? Why don't you make nice?" The immediate result was $5m for playing Elle Woods in Legally Blonde, a hit of such proportions that two years later she was Elle again in Legally Blonde 2 for $15m.

Now she is a divorced mother of two with an Oscar for charming us all as June Carter Cash in Walk the Line. She was the spine of a loose film. Still, next to Tracy Flick and Vanessa Lutz, this was conventional stuff. She's tried period (Vanity Fair and The Importance of Being Earnest) and she's tried soupy romance: (Just Like Heaven). But she's a star and Rendition (a very worthy attempt at its tough subject) is the kind of careful film that stars make.

So cross your fingers. Reese Witherspoon has all the confidence to play nasty girls and demon insurrectionaries. But you don't get $15m a time for those outsiders. I think even her admirers have to face the possibility that, without dynamic comic material, that fabulous teenage sneer could turn into a sugary smile.

For previous entries in the Biographical Dictionary of Film click here.